The present invention generally relates to magnetic recording of information and more particularly to a high-sensitivity magnetic head for use in a magnetic disk drive for reading information from a magnetic disk by utilizing magneto-resistive effect.
A magneto-resistive head that uses magneto-resistive effect for reading magnetic information from a magnetic disk has an advantageous feature in that it provides an output signal more or less independently to a scanning speed of the magnetic head over a magnetic disk, on which information is recorded in the form of minute magnetic dots. Thus, a magneto-resistive head is suitable for a use in high-density magnetic disk drives in which a magnetic head is required to reproduce information from magnetic dots that are recorded on the magnetic disk surface with high density and reduced mutual separation.
With the progress in the art of high-density magnetic recording, the demand imposed on a magnetic head for detection of high-density magnetic information is becoming more and more stringent. In order to reproduce information from minute magnetic dots formed on a magnetic disk with rapidly reduced bit length and track width, it is necessary to increase the sensitivity of the magnetic head accordingly.
FIG. 1A shows the construction of a magneto-resistive head 10 used in conventional high-density magnetic disk drives.
Referring to FIG. 1A, the magneto-resistive head 10 includes a magneto-resistive film 11 for detection of magnetic field, wherein the magneto-resistive film 11 changes a resistance thereof in response to a magnetic field applied thereto, and the magneto-resistive head 10 achieves the detection of the magnetic field by measuring the magneto-resistance of the magneto-resistive film 11.
For this purpose, electrodes 13A and 13B are provided on the magneto-resistive film 11 for causing to flow a sensing current through the magneto-resistive film 11, wherein the electrodes 13A and 13B are respectively provided on domain control regions 12A and 12B disposed at both lateral sides of the magneto-resistive film 11 for domain control of the magneto-resistive film 11. More specifically, the domain control regions 12A and 12B are formed of a hard magnetic material such as CoCr having a large coercive force or an anti-ferromagnetic film such as PdPtMn and eliminate formation of magnetic domains in the magneto-resistive film 11 takes a mono-domain structure, and Barkhausen noise, caused as a result of movement of domain walls, is effectively eliminated.
In the magneto-resistive head 10 of FIG. 1A, the magneto-resistive film 11 may be formed of a single-layer anisotropic magneto-resistive (AMR) film or a giant magneto-resistive (GMR) film, wherein the GMR film may be a spin-valve film or a tunneling magneto-resistive (TMR) film. A spin-valve film includes an anti-ferromagnetic pinning layer, a ferromagnetic pinned layer provided adjacent to the anti-ferromagnetic pinning layer, and a ferromagnetic free layer provided in the vicinity of the ferromagnetic pinned layer provided in the vicinity of the ferromagnetic pinned layer via an intervening non-magnetic conducting film. A TMR film includes an anti-ferromagnetic pinning layer, a ferromagnetic pinned layer provided adjacent to the anti-ferromagnetic pinning layer, and a ferromagnetic free layer provided in the vicinity of the ferromagnetic pinned layer via an intervening tunneling insulation film. In the case a GMR film or TMR film is used for the magneto-resistive film 11 in the magnetic head 10 of FIG. 1A, it should be noted that the domain control regions 12A and 12B control the domain formation in the ferromagnetic free layer by causing a localized pinning of magnetization in the ferromagnetic free layer.
In view of the fact that the domain control regions 12A and 12B achieve the desired domain control in the ferromagnetic free layer by causing a local pinning of magnetization as noted above, there are formed dead regions in the magneto-resistive film 11 designated as INS in FIG. 1A in which the magnetization of the free layer does not change substantially even when a magnetic field from a magnetic dot on the magnetic disk is applied.
In the construction of FIG. 1A, the sensing current from the electrode 13A to the electrode 13B inevitably flows through a path that crosses the dead regions INS and the sensitivity of magnetic detection is deteriorated.
In view of the drawback of the magnetic head 10 of FIG. 1A, there is proposed a magneto-resistive head 20 having a so-called overlaid structure as represented in FIG. 1B, in which electrodes 23A and 23B respectively corresponding the electrodes 13A and 13B are provided on domain control regions 22A and 22B respectively corresponding to the domain control regions 12A and 12B of FIG. 1A, such that each of the electrodes 23A and 23B includes a tip-end region 23A-a or 23B-b that extends over a magneto-resistive film 21 in the direction of the other, opposing electrode, beyond the dead region INS. According to the construction of the magneto-resistive head 20 of FIG. 1B, the sensing current flows through the magneto-resistive film 21 corresponding to the magneto-resistive film 11 while avoiding the dead regions INS, and the sensitivity of the magneto-resistive sensor 20 is improved.
Further, there is proposed a magneto-resistive head 30 having a CPP structure as noted in FIG. 2, in which the sensing current is caused to flow perpendicularly to a magneto-resistive film 31.
Referring to FIG. 2, it can be seen that domain control regions 32A and 32B are provided at both lateral sides of the magneto-resistive film 31 for magnetic domain control, wherein the sensing current is caused to flow through the magneto-resistive film 31 perpendicularly between an upper electrode 33A provided on the magneto-resistive film 31 and a lower electrode 33B provided under the magneto-resistive film 31. The magnetic head 30 having the CPP construction noted above is advantageous for high-sensitivity detection of the magneto-resistance change caused by an external magnetic field. In the magneto-resistive head 30, too, it is possible to use a GMR film such as a spin-valve film or TMR film for the magneto-resistive film 31.
On the other hand, the magneto-resistive head 30 of the CPP structure of FIG. 2 has a drawback, while being able to increase the sensitivity of the magneto-resistive film 31 itself, in that the dead regions INS are formed within the path of the sensing current as a result of local magnetic pinning action of the domain control regions 32A and 32B similarly to the magneto-resistive head 10 of FIG. 1A and that the existence of the dead regions INS in the sensing current path reduce the effective core width TW of the magneto-resistive film 31 used for magnetic detection. Because of the reduced effective core width TW, the magnetic head 30 can detect only a part of the magnetic information recorded on a magnetic track of the magnetic disk even in such a case where the magnetic head 30 has a geometrical or so-called optical core width corresponding to the track width on the magnetic disk. Further, the dead regions INS tend to cause a disturbance in the sensing current flowing through the magneto-resistive film 31 perpendicularly.
In the case of the magneto-resistive head 20 of FIG. 1B, on the other hand, the problem of the sensitivity degradation caused by the dead regions INS is avoided successfully by providing the protruding tip-end regions 23A-a and 23B-b for the electrodes 23A and 23B such that the sensing current is caused to flow preferentially in the geometrical or optical core region defined between the opposing tip-end regions 23A-a and 23B-b, as noted before.
On the other hand, the magneto-resistive head 20 of FIG. 1B has a drawback in that the protrusion of the tip regions 23A-a and 23B-b beyond the dead regions INS tends to cause an increase in the effective core width TW over the geometrically defined optical core width, as a result of the distribution profile of the sensing current formed underneath the tip-end regions 23A-a and 23B-b protruding beyond the dead regions INS. It should be noted that exact control of the process for forming the electrodes 23A and 23B with the tip-end regions 23A-a and 23B-b in exact alignment with the inner edge of the dead region INS has been difficult. Further, the magneto-resistive head 20 of FIG. 1B tends to suffer from the problem of positional offset of the tip regions 23A-a and 23B-b with respect to the core region TW. It should be noted that the domain control regions 22A and 22B are formed by a process different from the process of forming the electrodes 23A and 23B, and because of this, it is generally inevitable that such a positional offset is caused.